In medicine, “adherence” (also compliance or capacitance) describes the degree to which a patient correctly follows medical advice. Most commonly, it refers to medication or drug compliance, but it can also apply to other situations such as medical device use, self care, self-directed exercises, or therapy sessions.
Worldwide, non-compliance is a major obstacle to the effective delivery of health care. Estimates from the World Health Organization (“WHO”) in 2003 indicate that only about 50% of patients with chronic diseases living in developed countries follow treatment recommendations. The figures are even lower with respect to adherence rates for preventative therapies, and can be as low as 28% in developed countries. In particular, low rates of adherence to therapies for asthma, diabetes, and hypertension are thought to contribute substantially to the human and economic burden of those conditions. This may affect patient health, and affect the wider society when it causes complications from chronic diseases, formation of resistant infections, or untreated psychiatric illness.
Compliance rates may be overestimated in the medical literature, as compliance is often high in the setting of a formal clinical trial but drops off in a “real-world” setting. For example, one study reported a 97% compliance rate at the beginning of treatment with statins, but only about 50% of patients were still compliant after six months.